1. Field of the Invention
This invention relates to a liquid crystal display module, and more particularly to a liquid crystal display module and a driving method thereof that reduce the thickness and the weight of the module and improve the picture quality of the liquid crystal display.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) includes a liquid crystal display module, and a driving circuitry for driving the liquid crystal display module.
The liquid crystal display module consists of a liquid crystal display panel having liquid crystal cells arranged in a matrix between two glass substrates, and a backlight unit for irradiating a light onto the liquid crystal display panel. The liquid crystal display module includes optical sheets for vertically raising a light propagating from the backlight unit toward the liquid crystal display panel.
In the related art liquid crystal display panel, the backlight unit and the optical sheets must be integrally engaged with each other to prevent loss of light, and to protect from damage caused by an external impact. To this end, the LCD panel includes a case that encloses the back light unit and the optical sheets, including the edge of the liquid crystal display panel.
FIG. 1 is a perspective view of a structure of a liquid crystal display module according to related art. FIG. 2 is a section view of the liquid crystal display module taken along the II-II′ line in FIG. 1. Referring to FIG. 1 and FIG. 2, the related art liquid crystal display module 1 includes a main support 14, a backlight unit, a liquid crystal display panel 6, and a top case 2. The liquid crystal display panel 6 is disposed at the inside of the main support 14. The top case 2 encloses the edge of the liquid crystal display panel 6 and the main support 14.
A liquid crystal is injected between an upper substrate 5 and a lower substrate 3 of the liquid crystal display panel 6. The liquid crystal display panel 6 includes a spacer (not shown) to maintain a constant gap between the upper substrate 5 and the lower substrate 3. The upper substrate 5 of the liquid crystal display panel 6 is provided with a color filter, a common electrode and a black matrix, etc (not shown). A signal wiring such as a data line and a gate line, etc. (not shown) is formed at the lower substrate 3 of the liquid crystal display panel 6, and a thin film transistor (TFT) is formed at an intersection between the data line and the gate line.
The TFT switches a data signal to be transmitted from the data line into the liquid crystal cell in response to a scanning pulse (i.e., a gate pulse) from the gate line. A pixel electrode is formed at a pixel area between the data line and the gate line. One side of the lower substrate 3 includes pad areas connected to the data lines and the gate lines. A tape carrier package (not shown) is attached onto the pad area. The tape carrier package includes a driver integrated circuit for applying a driving signal to the TFT. This tape carrier package applies data signals from the driver integrated circuit to the data lines. The tape carrier package also applies scanning signals to the gate lines.
An upper polarizing sheet is attached onto the upper substrate 5 of the liquid crystal display panel 6. A lower polarizing sheet is attached onto of the rear side of the lower substrate 3 of the liquid crystal display panel 6.
The main support 14 is a molded product. An inner side wall surface of the main support is molded into a stepped coverage face. This stepped coverage face is provided with a securing part to which a plurality of optical sheets 8 is safely secured. A back light unit, first and second light guide plates 10 and 20, a reflective sheet 12, and a plurality of optical sheets 8 are disposed at the inner side layer of the main support 14. The backlight unit comprises light emitting diode (LED) arrays 30a and 30b for irradiating a light onto the liquid crystal display panel 6. The reflective sheet 12 is arranged at the rear side of the first light guide plate 10. The optical sheets 8 are disposed between the second light guide plate 20 and the liquid crystal display panel.
FIG. 3 is a perspective view of a general light emitting diode array. As shown in FIG. 3, the LED array 30 of the related art backlight unit includes a plurality of LED's for generating lights, and a printed circuit board (PCB) including a circuit for controlling an emission of the plurality of LED's 34. The LED 34 is a point light source that emits a red light, a green light and a blue light. The PCB 32 supports the LED 34 and controls an emission of the LED 34 by a circuit configured thereon. A light generated from the LED 34 is incident upon the first and second light guide plates 10 and 20 through the incidence faces of the first and second light guide plates 10 and 20.
The light propagated into the bottom and the side of the LED array 30 is reflected by the reflective sheet 12 to be progressed toward the output face. The light output via the first and second light guide plates 10 and 20 is incident, via the plurality of optical sheets 8, to the liquid crystal display panel 6.
The reflective sheet 12 is located at the rear side of the first light guide plate 10, and reflects a light incident thereto through the rear side of the first light guide plate 10 into the light guide plate 10, thereby reducing loss of light. In other words, when light from the LED 34 is incident onto the light guide plates 10 and 20, then light propagated toward the bottoms and the sides of the light guide plates 10 and 20 is reflected by the reflective sheet 12 toward the liquid crystal display panel 6.
The first and second light guide plates 10 and 20 convert a straight line of light input from the LED arrays 30a and 30b into a surface light to thereby guide the light into the liquid crystal display panel 6. The bottoms of the first and second light guide plates 10 and 20 include printed patterns 15 and 25. The printed patterns have a convex shape. The patterns are printed at positions separated by a desired distance from the incidence faces of the first and second light guide plates 10 and 20.
A light beam going through the light input part is reflected at a desired incline angle from the rear side provided with the printed patterns 15 and 25 to propagate uniformly toward the output face. The above-mentioned arrangement of the printed patterns insures that a distance “d” is adequate for combining red, green and blue lights emitted from the LED arrays 30a and 30b to generate white light.
A light incident onto the liquid crystal display panel 6 has a higher light efficiency when it forms a right angle. The plurality of optical sheets 8 vertically raises a light output from the first light guide plate 10 to thereby improve light efficiency. To this end, the liquid crystal display module includes a lower diffusing sheet for diffusing light output from the first and second light guide plates 10 and 20 into the entire area, first and second prism sheets for raising a propagation angle of the light diffused by the lower diffusing sheets vertically with respect to the liquid crystal display panel 6, and an upper diffusing sheet for diffusing light going through the first and second prism sheets. Thus, light output from the first and second light guide plates 10 and 20 is incident onto the liquid crystal display panel 6 via the plurality of optical sheets 8.
The top case 2 is shaped into a square band having a plane part and a side part, each of which is bent perpendicularly. The top case 2 encloses the edge of the liquid crystal display panel 6 and the main support 14.
Typically, the backlight unit is small, thin and lightweight. Accordingly, such LED arrays 30a and 30b, as shown in FIG. 2, are convenient light sources for a general backlight unit because of their low power consumption, thin shape, light weight and brightness, etc. as compared to a lamp.
The LED arrays 30a and 30b include a plurality of LED's 34a and 34b for generating lights 36a and 36b, respectively, and PCB's 32a and 32b mounted with a circuit controlling an emission of the plurality of LED's 34a and 34b, respectively. The plurality of LED's 34a and 34b are point light sources that emit a red light, a green light and a blue light. Such LED's 34a and 34b are arranged at the sides of the first and second light guide plates 10 and 20 to responsible for light sources.
The lights 36a and 36b generated from the plurality of LED's 34a and 34b are incident onto the first and second light guide plates 10 and 20 via the incidence faces of the first and second light guide plates 10 and 20. As mentioned above, since the plurality of LED's 34a and 34b generates red, green and blue lights, a desired distance “d” is required for combining the red, green and blue lights to convert them into a white light. For this reason, scattering patterns 15 and 25 provided at the first and second light guide plates 10 and 20 are formed at a desired distance “d” for combining red, green and blue lights emitted from the LED's 34a and 34b to convert them into a white light from the incidence faces of the first and second light guide plates 10 and 20.
The lights 36a and 36b emitted from the plurality of LED's 34a and 34b are scattered by the scattering patterns 15 and 25 provided at the first and second light guide plates 10 and 20 to have a propagation direction towards the liquid crystal display panel 6. If the plurality of LED's 34a and 34b emitting red, green and blue lights are used as light sources, then a partial area of the first and second light guide plates 10 and 20 is used as a region in which the red, green and blue lights are combined to be converted into a white light and the brightness of lights output from the first and second light guide plates 10 and 20 is scattered only at the remaining area.
In order to solve this problem, the first and the second light guide plates 10 and 20 are used to distribute uniformly a brightness of a light irradiated onto the liquid crystal display panel 6, as depicted in FIG. 2. In other words, a light 36a emitted from the LED 34a arranged at the side of the first light guide plate 10 is scattered by the scattering pattern 15 provided at the first light guide plate 10. A propagation direction of the scattered light 38b is changed towards the liquid crystal display panel 6.
The above-mentioned backlight unit of the liquid crystal display module suffers from the following drawbacks. The backlight unit has a large thickness “d1” because the light guide plates 10 and 20 are used to uniformly distribute the brightness. Thus, a weight of the backlight unit increases accordingly. Furthermore, a brightness of the light 38a output from the first light guide plate 10 is reduced accordingly because of the propagation through the second light guide plate 20. Such a brightness reduction phenomenon deteriorates the display quality of the liquid crystal display module 1.
Moreover, the performance of above-mentioned backlight unit of the liquid crystal display module 1 is affected by the driving of a light source, for example LED 34, in a hold-type driving method. In the hold-type driving method, the light source is continuously turned on, thereby causing large power consumption. Hence, LED 34 dissipates heat, thus causing a reduction in the life the LED 34. In addition, the LCD suffers from a blur phenomenon due to such a hold-type driving of the LED 34. As depicted in FIG. 4, a picture becomes cloudy, thereby deteriorating the display quality of the liquid crystal display module 1.